I have a number of images in my HTML document.
The user triggers some changes (AJAX calls) when clicking on an image or by pressing a key.
To keep track of the latest image (client-side), I use javascript and onmouseover, assigning the image ID to a javascript-variable which in turn is used to fill the AJAX calls.
Everything works well (even it there might be better ways to do it), but sometimes it takes some time to refresh the image. For a moment, it ceases to exist, causing the image next to it to jump left.
This, of course, moves that image underneath the pointer, triggering the mouseover event.
How(?) is it possible to distinguish between a mouseover event caused by mouse-movement from one fired by a layout change?
The short answer is you can't really tell what caused a mouseover event, other than the cursor moved over a new DOM element (or some other things, like a tap on a touch device). A layout change is just something that happens independent of this event.
One possible solution to your actual problem is to avoid the problem altogether by preventing the layout jump. For example, you could use a placeholder element to fill the space while the next image loads.
Alternately, your logic could almost-certainly be made more-robust so as not to depend on something as fragile as this.